Oil Level and Fuel Economy

[MadMax]

OK, I have been interested in the level of oil most people keep their Yaris at since I have been trying to find ways to counter the "winter gas syndrome" that has dropped my MPG average (from 36-38 MPG during the summer to 32-34 during the winter. Note I am running 215/45ZR17s Riken Raptors on my 08 auto hatch).

I came across this web site: Exstrom Laboratories - How To Increase Your Gas Mileage and note FAQ #22 states:

Can a low engine oil level reduce my gas mileage?
Yes it will. A low oil level increases engine friction, and so reduces gas mileage.

But my question is does keeping your oil level at half or below on the dip stick help increase gas mileage? Mine is usually close to the upper point on the stick, and if anyone has any firsthand experience with keeping it lower I would like to hear their results.

Cheers! M2